The weather is warming and the fish are swimming – some of them longer and further than they have in nearly two centuries. Last week was World Fish Migration Day (May 21st), a day when people around the world celebrate fish that travel long distances through a variety of waterways. This year, the day included 450 events in 75 countries.

More locally, groups in Maine gathered to celebrate the restoration of some of the state’s alewife populations. Alewives (Alosa pseudoharengus) is the more common of two species that are referred to as river herring. The other is the Blueback Herring (Alosa aestivalis). Both species are small silvery fish, and they are very hard to tell apart. Alewives have a slightly bigger eye and a bronze-colored head, whereas blueback herring have a smaller eye and a silvery head.

While they are both referred to as river herring, both Alewives and Blueback Herring only spend part of their lives in rivers. The reason that they are celebrated on World Fish Migration Day is that they spend the other part of their lives in the ocean. These small fish form large schools in the spring and travel from their adult homes in saltwater up into fresher water of tributaries, streams and rivers, and eventually into lakes and ponds where they will spawn. Then, the “spent” adults travel back towards the sea, as also eventually do the new generation of fish.

River herring populations were once abundant and supported fisheries along the coast. People used drift nets, hand nets, and constructed weirs to catch them. Then, they were smoked and eaten or used for bait to catch larger, more valuable species. But their abundance depended on both the health of the water and also the connectivity between their spawning and “adulting” grounds. Without the ability to get upstream to spawn, there can be no next generation of river herring.

Pollution in waterways due to industrialization including the construction of mills along rivers that used harmful chemicals in their production of paper or textiles threatened these and other fish populations. In addition, the use of river power for electricity and to run those same mills led to building dams to harness the energy of several of Maine’s major rivers. These two major factors led to the herring population declining to nearly endangered levels.

Fortunately, since then, efforts have been made both to clean up the water and to enable fish to travel along the necessary path to complete their life cycle and replenish their populations. The Clean Water Act of 1972, which recently celebrated its 50th anniversary, helped to provide funding for treatment facilities to improve water quality. And the removal of dams or construction of fish ladders restored passageways for these migratory fish.


We have a Fishway in Brunswick on the Androscoggin that was built in 1980 to help with the passage of migratory fish. It isn’t designed for herring, however, but does function to help endangered Atlantic Salmon, another migratory species, to travel upstream. It’s a good reminder that, while crossing from Brunswick to Topsham, you may feel like you are far from the ocean, but the river system connects through Merrymeeting Bay out into the sea.

There is another location much further from the coast, however, where a great celebration was held this year to welcome back the historical run of river herring. In the inland town of Vassalboro, people gathered at China Lake, part of the Kennebec River Estuary, to see throngs of alewives coming all the way into the lake to spawn. Through the efforts of Maine Rivers, a non-profit dedicated to the restoration of historic fish runs, the last seven miles between China Lake and the Kennebec River were

cleared for these incoming fish. The multi-year effort included the removal of three dams and construction of three fish ladders. When these fish arrived this spring, it was the first time since just after the Revolutionary War. Close to a million alewives returned.

Environmental restoration work can be frustrating and full of disappointment, as trying to reverse what has occurred in nature is never simple. But there are examples like this one that are heartening. The process of restoration was not quick, but for those who celebrated the abundance of herring arriving at China Lake, it was a heartening sign that it is possible to make a difference in bringing back an important species to Maine’s coast and waterways.

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